In an adaptation of her new biography Elizabeth the Queen: The Life of a Modern Monarch, out in the December issue of Vanity Fair, contributing editor Sally Bedell Smith recounts the courtship of Elizabeth and Prince Philip, writing that, while everything else in the life of Lilibet was laid out for her, she made the most important decision on her own. “She never looked at anyone else,” her cousin Margaret Rhodes tells Smith.

Elizabeth accepted Philip’s proposal on the spot in the summer of 1946, without even consulting her parents. Philip seemed equally smitten. Smith quotes from a letter Philip wrote to the Queen in which he wondered if he deserved “all the good things which have happened to me,” especially “to have fallen in love completely and unreservedly.” He mused, “Cherish Lilibet? I wonder if that word is enough to express what is in me.” Philip declared that his new wife was “the only ‘thing’ in this world which is absolutely real to me and my ambition is to weld the two of us into a new combined existence that will not only be able to withstand the shocks directed at us but will also have a positive existence for the good.”

What didn’t make Philip as happy was Elizabeth’s decision to keep the Windsor name for her and her children. Queen Mary and the Queen Mother, backed by Winston Churchill, had persuaded her to do so. “She was very young…. Churchill was elderly and experienced, and she accepted his constitutional advice.” Philip’s cousin Patricia Brabourne tells Smith. According to Smith, the decision made Philip furious. “I am the only man in the country not allowed to give his name to his children,” Philip fumed to friends. “I’m nothing but a bloody amoeba.”

It remained a sore subject for years. When Prime Minister Harold Macmillan visited the Queen in January 1960, she told him that she needed to revisit the issue of her family name. “The Queen only wishes (properly enough) to do something to please her husband—with whom she is desperately in love,” the prime minister wrote in his diary. According to a telegram from Deputy Prime Minister Rab Butler to Macmillan, the Queen had “absolutely set her heart” on making a change for Philip’s sake. A compromise was reached: the royal family would continue to be called “the House and Family of Windsor,” but the Queen’s “de-royalised” descendants would adopt the surname “Mountbatten-Windsor.” Elizabeth announced the change on February 8, 1960, saying, “The Queen has had this in mind for a long time and it is close to her heart.”